1. Field of the Invention
The present invention relates to a sheet conveying device that conveys various kinds of sheets, more specifically, relates to a sheet conveying device that conveys a manually fed sheet.
2. Description of the Related Art
Conventionally there has been utilized an image forming apparatuses that forms an image on a various kinds of manually fed sheets such as a small-size sheet, a nonstandard-size sheet, thick paper and thin paper, which cannot be fed in a paper feeding cassette.
Further, there is a case where a sheet such that an image is already formed on one surface thereof, so-called backing paper, is manually fed for the purpose of reuse of a sheet. Backing paper easily causes sheet obstruction, that is, a jam in an image forming apparatus, because a curl, a fold or the mark of a stapler is formed on backing paper.
Japanese Unexamined Patent Publication JP-A 9-278243 (1997) discloses a technique for straightening a curl by curling rolled recording paper in a specified manner. According to this technique, by nipping a leading end of the recording paper with nip portions of a feed roller and a sponge roller, a curl in a rolled direction of the rolled recording paper is straightened, and a jam and a skew in a conveying path are prevented.
Further, Japanese Unexamined Patent Publication JP-A 2000-351491 discloses a technique for supplying a rolled sheet. In this technique, a sheet releasing separator which releases the leading end of the sheet rolled like a roll is used. The sheet releasing separator is divided into plural parts, and energized by springs. Consequently, even when the tip of the rolled sheet is curled, or even when the section of the recording paper is not good, the recording paper is stably conveyed, and occurrence of a jam is prevented.
The aforementioned art is a technique relating to a rolled sheet, and it is assumed that the paper quality of the sheet is constant at all times. Therefore, there is no description of prevention of a jam of sheets of different paper qualities or backing paper on which a fold or the mark of a stapler is formed. Accordingly, it is difficult to prevent a jam of various kinds of manually fed sheets by the aforementioned art.
For example, even if it is tried to curl sheets to prevent a jam as in JP-A 9-278243, manually fed sheets are curled too much or too little because the paper qualities thereof are not constant, and a jam occurs after all. Moreover, it is difficult to curl to prevent a jam in the case of a sheet whose tip is folded. Furthermore, in the case of guiding a sheet by the use of a plurality of separators as in JP-A 2000-351491, there is a fear that a sheet jams on a downstream side of the separators in the sheet conveying direction when a skew of the tip of the sheet is not solved.
Accordingly, in the aforementioned related arts, in a case where an arbitrary kind of sheet such as a manually fed sheet is fed, there is no guarantee that it is possible to convey while preventing a jam. In a case where a jam occurs inside an apparatus, it takes time and effort to solve the jam. Moreover, in a case where a jam frequently occurs inside an apparatus, the life thereof gets shortened, and it becomes hard to carry out maintenance. Furthermore, these problems also occur generally in sheet processing apparatuses equipped with sheet conveying devices.